The invention relates to a single-to-differential converter for generating two balanced output signals from one single ended input signal.
In analog circuits, particularly in CMOS circuits, improvement of performance can be achieved by using a balanced architecture. If two signals are fully balanced, i.e. if the two signals have equal amplitude and an exact 180 degrees phase shift is present between the two signals, even non-linearities are strongly reduced in the circuits. Furthermore, in modem integrated systems mixed analog and digital signals are present and crosstalk from digital to analog parts of the system, e.g. by substrate bouncing, becomes a serious problem. A circuit with a balanced architecture is much less sensitive to crosstalk compared to a single ended equivalent. A further advantage of a balanced architecture is that signal inversion is simply achieved by cross-coupling two signals.
A general problem is the making of two balanced signals from one single ended signal having low distortion and good balancing at high frequencies. Commonly a simple differential pair structure is used having one input coupled to the single ended signal and the other input coupled to a fixed DC voltage. A problem in the differential pair is that the inverting and non-inverting output signals of the differential pair have unequal delays in respect of the input signal due to the capacitance present at the common node of the differential pair. This results in output signals having a phase difference unequal to 180 degrees.